#include <cstdio>
FILE *f=fopen("nunta.in","r");
FILE *g=fopen("nunta.out","w");
unsigned char a[220],b[220];
short n,i,j,t,z;

int main()
{
    fscanf(f,"%d",&n);
    if (n<=3){
        fprintf(g,"%d",n);;
        return 0;
    }
    a[0]=1;a[1]=2;
    b[0]=1;b[1]=3;
    for (i=4;i<=n;i++) {
        t=0;z=0;
        for (j=1;j<=b[0]+1;j++) {
            t=a[j]+b[j]+z;
            z=0;
            if (t>9) {
                z=t/10;
                t%=10;
            }
            a[j]=b[j];
            b[j]=t;
        }
        a[0]=b[0];
        if (b[b[0]+1])
            b[0]++;
    }
    for (i=b[0];i>=1;i--)
        fprintf(g,"%c",b[i]+'0');
    return 0;
}